Influence of temperature on the coercive field of non-interacting fine magnetic particles

The Neel model of relaxation in a two level system was used in order to study the influence of temperature on the hysteresis loops of single-domain magnetic particles presenting uniaxial anisotropy and coherent magnetization reversal. Following the same line as the work by Stoner and Wohlfarth, the dependence of the coercive field on temperature for every possible orientation of the easy axis with respect to the field was studied. This study was then extended to include samples composed of many randomly oriented particles, concluding that the thermal dependence of the coercive field in these samples is not the frequently used T(1/2) dependence, which is valid only when the easy directions of the particles are oriented parallel to the magnetic field, but T(3/4). The model also facilitates the calculation of the dependence of the coercive field on other parameters, including the size of the particles or the characteristic measuring time. (C) 1998 Elsevier Science B.V. All rights reserved.